- Oligometastatic tumors with > 80% of measurable tumor volume in the target lung In both of the above situations, no clinical evidence of central nervous system (CNS) metastases can exist; oligometastatic disease is difficult to define but would, as a guideline, have only 1-4 loci of disease established in 1-2 organ systems outside the affected lung; exceptions to these guidelines can occur, particularly in cases where sites of metastatic disease are equivocal or so minute that it would not exceed 20% of tumor volume